Table of Contents
Reviewed and updated by ICD - Week 29/2026
Quick summary:
- Kraft liner is the kraft paper used as the outer and/or inner facing of corrugated cardboard. It is the main load-bearing layer, resisting impact, abrasion and moisture.
- Technical traits: high grammage (usually 150 g/m2 and up) and superior box compression strength (BCT).
- Two main types: virgin kraft liner (highest quality) and recycled kraft liner.
- Key role: it decides a carton’s stacking strength and print quality - vital in logistics, heavy-goods transport and long-term storage - and is used as the outer shell of kraft dunnage bags.
What is kraft liner? Its core role in carton structure
Kraft liner is the flat, smooth kraft sheet used as the outer face, inner face and sometimes the middle layer of corrugated board. It is the base material that defines the packaging’s load-bearing properties. For the fundamentals of the paper itself, see what kraft paper is.
Position and main technical function
Corrugated board combines three paper layers, and the kraft liner takes the main load-bearing role:
- Liner layer (kraft liner): the outermost and innermost layers. It resists compression when cartons are stacked (directly affecting BCT), provides a hard surface that protects the softer fluting inside from physical impact, and offers the flat, stable surface needed for printing logos and product information.
- Fluting layer: the middle paper, corrugated to create air gaps that cushion shock and bear axial load.
Technical specifications
Kraft liner usually runs from 150 g/m2 to over 450 g/m2 - higher grammage means greater stiffness, durability and static load capacity. It must have a high edge crush strength (ECT) to maximize the carton’s stacking ability. Premium kraft liner is often given a hydrophobic treatment or PE coating for better waterproofing and moisture resistance, protecting cartons in damp warehouses or on sea voyages. See the kraft paper grammage guide for how GSM maps to strength.
Types of kraft liner: pros and cons
Virgin kraft liner
Made from 100% virgin pulp (long cellulose fibers) via the Kraft process. It has the highest mechanical strength - long fibers give maximum tensile and compression strength - plus high uniformity, few impurities and accurate grammage for good print quality. Used for cartons needing very high compression strength, heavy international shipping and food-contact packaging.
Recycled kraft liner
Made from recovered pulp (used paper, old cartons). It is cheaper and more eco-friendly, but its strength is lower because fibers break during recycling, and it is more moisture-sensitive and may contain impurities. Used for cartons that do not need very high stacking strength, domestic packaging, and the inner face of cartons.
Kraft liner’s role in packaging quality control
Box compression (BCT) and edge crush (ECT)
The edge crush test (ECT) measures resistance to compression along the carton material’s edge. Kraft liner accounts for about 70% of total ECT - the higher its grammage and quality, the higher the ECT. The box compression test (BCT) measures vertical compression resistance when cartons are stacked, and is calculated largely from ECT. In short, better kraft liner means a stronger, more stackable box.
Why it matters for dunnage bags
High-grammage kraft liner is exactly the material used to build the multi-ply outer shell of kraft dunnage bags. The same strength that lets a carton stack high lets a dunnage-bag shell resist the dynamic compression of a shifting container load.
Frequently Asked Questions (FAQ)
What is the difference between kraft liner and fluting?
Kraft liner is the flat facing layer that bears load and takes print; fluting is the wavy middle layer that cushions shock. The liner provides most of the carton’s strength.
Virgin or recycled kraft liner - which should I choose?
Choose virgin for heavy international shipping, high stacking and food contact. Recycled is fine for domestic packaging and inner facings where cost matters more than maximum strength.
What grammage is typical for kraft liner?
From 150 g/m2 to over 450 g/m2. Higher grammage gives greater stiffness and a higher ECT and BCT.
Does kraft liner resist moisture?
Standard liner absorbs moisture, but premium grades are hydrophobic-treated or PE-coated for waterproofing in damp storage or sea freight.
Contact ICD Viet Nam
For kraft dunnage bags and packaging advice, contact our team for specifications and a quote.
- Northern Vietnam: 0983 797 186 / 090 345 9186 / 090 5859 186
- Southern Vietnam: 098 6784 186
- Email: sales@icdvietnam.com.vn
- Zalo: Chat on Zalo
Kraft Liner vs PP Woven in Dunnage Bag Outer Shells
The outer shell material is the single biggest factor in how a dunnage bag performs in real freight conditions. Kraft liner - made from wood pulp processed by the kraft (sulfate) method - has been the traditional choice for decades. PP woven fabric, made from polypropylene polymer strips woven into a textile, emerged as an alternative specifically for sea freight and humid environments. The table below compares the two materials across the five properties that matter most to procurement and logistics teams.
| Property | Kraft Liner | PP Woven |
|---|---|---|
| Base material | Softwood or hardwood pulp (kraft/sulfate process) | Polypropylene polymer |
| Weight range | 70-120 gsm per ply | 80-150 gsm total |
| Moisture resistance | Low - absorbs moisture and loses strength when wet | High - hydrophobic, unaffected by humidity |
| Tensile strength | Moderate - increases with number of plies | High - woven structure distributes load evenly |
| Cost | Lower base cost | Higher by 15-25% per unit |
For domestic road freight in dry conditions, kraft liner dunnage bags at Level 1 or Level 2 remain a cost-effective choice. The moisture disadvantage only becomes critical when the cargo moves through humid port environments or spends days inside a sealed ocean container where condensation builds up. PP woven bags carry a 15-25% price premium but eliminate moisture risk entirely, making the cost difference small relative to a cargo damage claim.
Frequently Asked Questions
What is kraft liner in the context of dunnage bags?
Kraft liner is the heavy-duty paper used as the outer shell of paper-based dunnage bags. It is made using the kraft (sulfate) pulping process, which breaks down wood fibers with sodium hydroxide and sodium sulfide to preserve long cellulose chains - the source of its higher tensile strength compared to standard paper grades. The word “kraft” comes from the German word for “strong.” In dunnage bag construction, individual sheets of kraft liner are laminated in multiple plies to reach the lateral force resistance required by each performance level, with individual ply weights typically ranging from 70 to 120 gsm.
How many layers of kraft liner does a dunnage bag need?
The number of plies depends on the performance level required by the load and transport mode. Level 1 bags typically use 1-2 plies of kraft liner and are suited for light loads in stable road conditions. Level 2 bags use 4 plies to handle heavier lateral forces, while Level 3 bags use 6 plies for the most demanding applications such as heavy industrial cargo or rail freight. More plies increase lateral force resistance and burst pressure, but also add weight and cost - which is one reason procurement teams specify the correct level rather than defaulting to the heaviest option available.
Why are kraft liner dunnage bags being replaced by PP woven?
Kraft paper absorbs moisture in humid or wet environments and loses a significant portion of its tensile strength when wet. In sea freight, containers experience temperature swings that cause condensation to form on interior surfaces, creating a consistently humid environment throughout a voyage. PP woven fabric is hydrophobic - it repels water at the fiber level and maintains its structural integrity regardless of ambient humidity. For container shipping routes, particularly those crossing tropical or high-humidity zones, PP woven dunnage bags reduce the risk of shell failure mid-voyage. The 15-25% cost premium over kraft liner is typically justified by the lower claim rate on moisture-affected cargo.
